1. Field of the Invention
The present invention relates to an electronic element and, particularly, to a novel organic semiconductor element which uses a conjugated high molecular compound, more particularly, to a field-effect transistor which uses an organic semiconductor.
More specifically, the invention relates to an electronic device which utilizes the main-chain conduction of a conjugated high molecular compound which is orientation controlled at a molecular level.
2. Related Background Art
Organic semiconductors have various possibilities, such as the realization of low cost processes and flexible devices, and recent years have seen very active research and development aimed at the application of electronic devices, such as electroluminescence elements and field-effect transistors (FETs).
Organic semiconductors used in electronic devices are broadly divided into low molecular compounds and high molecular compounds.
For example, complexes, such as copper and phtalocyanine, and polycyclic organic compounds, such as pentacene, are used as low molecular compounds, and thin film designs are obtained by techniques such as evaporation, whereby devices are fabricated.
In contrast to low molecular compounds, high molecular compounds have a structure in which conjugated double bonds are continuous as in polythiophene, polypyrrole, polyacetylene and the like, and they are used in fabricating devices by techniques such as printing.
In the case of low molecular compounds, almost all molecules have a structure in which the molecules are stacked due to interactions by Π electrons, and carriers migrate by hopping conduction among the molecules.
In many cases, in-plane orientation directions are at random. However, it has been reported that anisotropy in electrical conductivity can be observed by arraying molecules in a specific direction.
A technique which has accomplished an improvement in the characteristics of an FET by orienting low molecular compounds is disclosed in the Japanese Patent Application Laid-Open No. H07-206599, for example.
In conjugated high molecular compounds, ideally, Π electrons are delocalized throughout the molecules, and hence conjugated high molecular compounds have high carrier mobility within the molecules.
Among polymer chains, carriers migrate by hopping conduction.
At present, almost all polymer chains are used in a random condition in which they are not orientation controlled, and hopping conduction is a main conduction mechanism.
However, even in hopping conduction, it is possible to increase carrier mobility by aligning the orientation direction of molecules, and the Japanese Patent Application Laid-Open No. H09-246921 discloses a structure in which fibrils with aligned directions of polymer chains are formed so as to be orthogonal to the direction of an electrode.
Also, there have been proposed several techniques which involve providing protection from deterioration reactions and the like by introducing a conjugated high molecular compound as a guest into an inorganic or organic host material.
The object of these techniques is to prevent the attack of high molecular compounds by oxygen, water and the like.
A technique which uses cyclodextrin as a host material is disclosed in the Japanese Patent Application Laid-Open No. 2003-298067.
There are also several reports on techniques for introducing a conjugated high molecular compound into the pores of mesoporous silica.
In “Science,” Vol. 288, p. 652, there is a report to the effect that poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinnylene] (abbreviated as MEH-PPV), which is a conjugated polymer, is introduced in the mesopores of mesoporous silica monolith for which the orientation direction is controlled by the application of a ferromagnetic field.
However, the above-described techniques had several problems as described below.
That is, in the case of the method described in Non-patent Document 1, the mesoporous silica monolith contains many fine cracks and its application to electronic elements was difficult.
Also, the shown orientation distribution of pores was wide and it could not be said that the orientation controllability is high. Furthermore, the form of a monolith was not suitable for the fabrication of devices.